This invention is a novel torque-limiting apparatus particularly adaptable to power wrenches. It is a torque-responsive coupling operable in response to a selected torque load to break the driving connection between an input (driving) member and an output (driven) member. This invention further incorporates shut-off means for de-energizing the power supply in response to a pre-determined torque load.
Previously, clutch mechanisms incorporated with shut-off controls undesirably transmitted inertia forces, and were unduly sensitive to the "hardness" of a joint. Also, the prior mechanisms were found to be sensitive to many variables in addition to the joint hardness, such as air pressure in pneumatic tools, differences in lubrication of the fasteners and of the tools, and motor inertia. For example, reference may be made to U.S. Pat. Nos. 3,370,680, 3,515,251, or 3,195,704, each of which is believed to disclose mechanisms characterized by one or more of the aforementioned problems. In addition, torque-limiting devices from other areas of the art, such as U.S. Pat. Nos. 3,782,515 and 1,126,780 are believed to lack certain desirable features provided by the instant invention.
It is a principal object of this invention to provide an improved adjustable torque-limiting coupling that is relatively insensitive to variations in many variables that normally affect output torque.
It is a further object to provide an improved torque-limiting coupling that is easily adjustable for a pre-set torque and offers greater repeatable accuracy.
It is a further object of this invention to provide a novel adjustable torque-limiting coupling that can be used with a variety of shut-off devices to interrupt the flow of power to the power source.
Another object of this invention is the provision of an adjustable torque-limiting apparatus that is relatively straight-forward in construction, easy to maintain and repair, and dependable in operation.